Italian patent No. (application No. 20307 A/83) of the present applicant describes and claims a weft feeding device for weaving looms in which the system for stopping the weft yarn unwinding from the winding unit comprises one or more electromagnets which are disposed on a funnel-shaped cap, and which when energised cause their mobile armature to engage the conical zone of the winding drum and to interpose itself between this latter and the funnel, thus preventing the unwinding of further turns. According to said patent, the armature of these electromagnets, or their stopping pin, which is constructed of a wear-resistant material, collides with the conical zone of the winding drum, which is constructed of impact-resistant material and is able to deaden the impacts, thus preventing bouncing of the armature.
The electromagnets used for implementing and said stopping system in weft feeding device must be able to undergo hundreds of operations per minute and must comprise only small mobile masses in order to ensure a large acceleration and/or very small descent time for the armature. This requires a specially designed structure, which the present invention proposes by providing it with interesting constructional arrangements. Moreover, the present invention proposes to improve the weft yarn stopping system in weft feeding devices by ensuring operation under all working conditions and with any type of weft.
With regard to the first aspect, it should be noted that the most stressed part of the electromagnet is its mobile armature, which is subjected to high impact and inertial forces and comprises easily fractured critical zones in the armature shank (the mobile armature is not always perfectly orthogonal to the axis of movement of the shank, so that a bending stress can develop in the shank 5 which favours its fracture) and at the shank retention head of said armature due to the effect of its impact against the travel arresting means, even though damping elements are present. A structure with special constructional arrangements must therefore be conceived to overcome these problems.
With regard to the second aspect, it has been noted that in some cases, when particular yarns are present, the weft yarn tends sometimes to pass between said stopping pin and its resting zone on the drum cone due to imperfect contact between the surface of this latter and the end of the pin, or due to wear of said surface as a result of continual rubbing of the yarn. It is therefore desirable to modify the yarn stopping system in order to improve its stopping reliability.